Ink tank, head cartridge and ink jet printing apparatus

Abstract: A length (c) of a melamine foamed block (12) to be accommodated in an ink tank housing (11) as measured in the longitudinal direction is dimensioned to be larger than a length (C) of the ink tank housing (11) as measured in the longitudinal direction. Thus, while the foamed block (12) is accommodated in the ink tank housing (11), it is compressed in the direction orienting toward an ink feeding port (13) from which ink is fed to a printing head (14), i.e., in the ink feeding direction. Consequently, the ink retaining force induced by the capillary force is not intensified in the compressing direction of the melamine foamed block (12), resulting in an ink feeding capability of the printing head (14) being improved. On the contrary, the ink retaining force effective at a right angle relative to the compressing direction of the melamine foamed block (12) is intensified.

Description: The present invention relates to an ink tank for storably receiving ink therein according to the preamble of claim 1. Furthermore, the present invention relates to a head cartridge according to claim 26 and an ink jet printing apparatus according to claim 28 each of which comprises an ink tank according to the preamble of claim 1. Here, the printing operation represents all type of operations each to be performed for a various kind of ink receiving medium such as a cloth, a thread, a paper, a sheet-like material or the like so as to allow ink to be adhesively secured thereto. Therefore, the present invention can be applied to a printing apparatus, i.e., a printer serving as an information outputting apparatus operatively associated with a various kind of information processing apparatus. Many foamed blocks each molded of a polyurethane resin are hitherto used as an ink absorbing member to be accommodated in an ink tank of the foregoing type In the case that a urethane foamed block is used as an ink absorbing member, films are formed in the foamed block during each molding operation in such a manner as to wrap each of a number of voids (pores) in the foamed block with a film. Thus, since the voids are isolated from each other due to the presence of the film between adjacent voids, the foamed block can not exhibit a function of absorbing ink therein as it is. To cope with this problem, the foamed block is subjected to film removing treatment via heating, cleaning and others. However, it is very difficult to completely remove films in the foamed block with the film removing treatment as mentioned above. In most cases, a considerable amount of residue practically adheres to each void or pore on completion of the film removing treatment. In the case that the urethane foamed block is used as the ink absorbing member, it is usually accommodated in the ink tank in the compressed state. In addition, to assure that an adequate intensity of negative pressure acts on a communicating portion between the foamed block and a connecting member for an ink outflow portion while maintaining a certain pressure gradient across the foregoing communicating portion, a part of the foamed block is usually compressed at the communicating portion. However, since film residues remaining between adjacent voids or pores are liable to overlap in the foamed block, there arise malfunctions that ink hardly flows in the ink absorbing member, and moreover, ink fails to be fed outside of the ink tank. On the other hand, in contrast with the urethane foamed block, a generic ink absorbing member comprising a foamed block molded of a condensate composed of a melamine and a formaldehyde is described in the document WO-A 91/02652. The ink absorbing member as described in the above document is molded in the form of a skeleton having no thin film in each gap present in the circuit network of the foamed block while assuming a net-shaped structure. Thus, the ink absorbing member composed of a melamine foamed block has many advantages that any type of film removing treatment is not required, a large quantity of ink can storably be received in the melamine foamed block owing to the presence of a number of fine fibers constituting the circuit network compared with the urethane foamed block, initial ink filling treatment can easily be conducted owing to an excellent hydrophilic property of the melamine foamed block in contrast with the urethane foamed block having a water repelling property, no ink remains in the melamine foamed block having no film formed therein due to the presence of a residue on completion of ink consumption, and the ink in the melamine foamed block can completely be utilized at a high efficiency. Basically, it is preferable that the ink absorbing member composed of a melamine foamed block which is disclosed in the above-stated prior art document is practically used in the compressed state, and ink is fed to an ink outflow portion disposed at the lower part of an ink tank by the function of the gravity force of ink itself. Thus, the ink feeding direction orienting toward the ink outflow portion is firmly determined to coincide with the downward direction. For this reason, there arises a problem that an attitude to be assumed at the time of practical use of the ink tank described in the document is restrictively determined. In addition, in the case that the ink absorbing member is accommodated in the ink tank in the preferably employable uncompressed state, it is difficult that the ink absorbing member is brought in close contact with the inner wall surface of the ink tank. Thus, a gap is liable to appears between the ink absorbing member and the inner wall surface of the ink tank. When the atmospheric air taken through an atmospheric air communication port or an ink ejecting port of an ink jet head stays in the gap, there arises a malfunction that as ink is ejected from the ink jet head, a bubble is involved in the ink fed to the ink jet head, causing a quality of printed image to be remarkably degraded. Especially, with respect to an ink jet recording apparatus of the type including an ink tank and an ink jet head integrated with each other to perform a printing operation by reciprocably scanning the integrated structure composed of the ink tank and the ink jet head relative to a printing medium, there readily arises a problem that the ink tank is vibratively displaced due to the reciprocable scanning of the foregoing integrated structure. In the case that the ink jet printing apparatus is adversely affected by the vibrative displacement of the ink tank or in the case that the ink tank includes a member at the position located in the vicinity of an ink outflow portion, when a part of the ink absorbing member located in the vicinity of the ink outflow portion exhibits deterioration in terms of properties as time elapses, a gap is liable to appear at the above-noted part of the ink absorbing member. At this time, it is anticipated that the adverse influence given to the ink absorbing member due to staying of air at the gap becomes more remarkable. In an extreme case, it is preestimated that the atmospheric air communicating portion and the gap located in the vicinity of the ink outflow portion are communicated with each other. Once such a malfunction as mentioned above has arose, it becomes impossible to perform a desired ink ejecting operation, and moreover, the ink present in an ink feeding path leaks from an ink ejecting port, causing the interior of the ink jet printing apparatus to be contaminated with the leaked ink. Since feeding of ink to the ink outflow portion is achieved by utilizing the gravity force of the ink itself, when an ink jet head is driven at a high frequency highly desired in recent years, there is a possibility that the ink feeding can not follow the driving of the ink jet head at a high frequency. To improve a property of followability of the ink jet head at the driving of the latter at a high frequency, it is thinkable that a pore size is enlarged to some extent and a magnitude of resistance against flowing of the ink is reduced. In this case, however, there is a possibility that an ink retaining capability of the ink absorbing member is degraded, causing ink to leak from the atmospheric air communicating port. According to the description of the prior art document, in some case, it is desirable that a certain intensity of compressing force is applied to a foamed structure for the ink absorbing member in a specific application example of the ink jet printing apparatus in order to maintain useful or suitable properties of the ink absorbing member in the uncompressed state, and moreover, adjust a gap space of the foamed structure. It is considered that the description of the prior art document was made in consideration of the relationship between inner dimensions of the accommodating space and outer dimensions of the ink absorbing member. From the further prior art document EP-A-0 536 980 A2 an ink tank comprising an ink absorbing member is known. In the ink tank, the ink outflow portion is placed in the bottom area of the ink tank. The ink outflow portion and the ink inflow portion are disposed within a compression zone. In this zone the capillary force is high in order to suck ink via the ink inflow portion into the ink tank. The inventors of the present invention conducted a variety of examinations and as a result derived from the examinations, they found that it was acceptable that the ink absorbing member was properly compressed in order to assure that ink could smoothly and reliably be fed to the ink absorbing member regardless of an attitude assumed by the ink tank while utilizing advantages of the ink absorbing member molded of a condensate composed of a melamine and a formaldehyde. In addition, the inventors found the following technical problems to be solved. Specifically, one of the problems is that the ink absorbing member should be compressed corresponding to the structure of the ink absorbing member in a certain adequate direction in order to assure that ink can smoothly be fed to the ink absorbing member, other one is that so-called warpage or breakage is liable to occur at a compressible part of the ink absorbing member having a comparative brittle fibrous structure, and another one is that once the warpage has occurred with the ink absorbing member, the compressed state of the latter can not be maintained any more, resulting in the ink absorbing member assuming an uncompressed state. In addition, a filter is usually disposed at the ink outflow portion for removing foreign materials involved in the ink fed from the ink absorbing member, and an opening area of the ink outflow potion is determined corresponding to a quantity of ink to be fed therefrom. However, since the thermosetting melamine based condensate is brittle in structure, a part of the condensate is peeled away from the ink outflow portion when the ink absorbing member is worked, accommodated in the ink tank or put in later practical use, and the filter is clogged with fractured pieces of the condensate. In this connection, the inventors found another technical problem to be solved at this time, i.e., a problem that a desired quantity of ink to be fed could not be assured with the ink absorbing member. These technical problems mentioned above is not described in the prior art document WO-A 91/02652. The present invention has been made in consideration of the aforementioned background. The object of the invention is to provide an ink tank comprising an ink absorbing member which has an improved ink feeding capability. Furthermore, a head cartridge and an ink jet printing apparatus shall be provided each of which comprises the aforementioned ink tank. Moreover, there shall be provided an ink tank, a head cartridge and an ink jet printing apparatus wherein at least one of the technical problems as mentioned above can be solved by utilizing advantages obtainable from an ink absorbing member comprising a porous block having a three-dimensional net-shaped structure, i.e., a foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde. Another objective of the present invention is to provide an ink tank, a head cartridge and an ink jet printing apparatus wherein an ink feeding capability of the ink absorbing member can be improved by reducing only an intensity of ink retaining force effective in the ink feeding direction while unchangeably maintaining a predetermined intensity of ink retaining force on the assumption that the foamed block constituting the ink absorbing member to be accommodated in an ink tank is compressed in the direction orienting toward an ink feeding port, and a size of each of a number of pores in the foamed block orienting in the compressing direction does not vary but a pore size as measured at a right angle relative to the compressing direction is reduced. A further objective of the present invention is to provide an ink tank, a head cartridge and an ink jet printing apparatus wherein the ink absorbing member is effectively and adequately thrusted against the ink outflow portion, and a number of single fibers each having a high ink usage efficiency are employed for the ink absorbing member so as to enable ink to be easily filled in the ink absorbing member. The above-stated object is achieved by means of the combination of the features defined in claim 1. Preferred embodiments of the ink tank according to claim 1 are disclosed in the dependent claims 2 to 25, respectively. The ink tank according to claims 1 to 25 can be included in a head cartridge according to claim 26 as well as in an ink jet printing apparatus according to claim 28. A preferred embodiment of the head cartridge is disclosed in claim 27. According to a first aspect of the present invention, there is provided an ink tank for storably receiving ink therein, comprising: a housing having an ink feeding port formed therethrough so as to allow ink to be storably received therein to be fed through the ink feeding port; an ink absorbing member accommodated in the housing for retaining ink therein, the ink absorbing member being a porous block having a three-dimensional net-shaped structure and comprising a foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde as base materials; and compressing means for compressing the ink absorbing member toward the ink feeding port. According to a second aspect of the present invention, there is provided an ink tank for storably receiving ink therein, comprising: a housing having an ink feeding port formed therethrough so as to allow ink to be storably received therein to be fed through the ink feeding port; an ink absorbing member accommodated in the housing for retaining ink therein, the ink absorbing member being a porous block having a three-dimensional net-shaped structure and comprising a foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde as base materials; and compressing means for compressing the ink absorbing member in the housing at least in one direction. According to a third aspect of the present invention the ink tank for storably receiving ink therein further comprises a foamed block deforming/accommodating means for compensating or suppressing deterioration of properties of the ink absorbing member. According to a fourth aspect of the present invention, there is provided an ink tank for storably receiving ink therein, comprising; a housing; an ink absorbing member accommodated in the housing for retaining ink therein, the ink absorbing member being a foamed block including cell films of which number is smaller than that of a foamed block molded of a polyurethane resin or a foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde; and at least a part of the ink absorbing member accommodated in the housing for retaining ink therein being subjected to preliminary treatment for the purpose of compensation of the deterioration of property of the ink absorbing member. According to a fifth aspect of the present invention, there is provided head cartridge including a printing head for ejecting ink therefrom and an ink tank for storably receiving ink to be fed to the printing head, the printing head and the ink tank being integrated with each other, wherein the ink tank comprises: a housing having an ink feeding port formed therethrough so as to allow ink to be storably received therein to be fed through the ink feeding port; an ink absorbing member accommodated in the housing for retaining ink therein, the ink absorbing member being a porous block having a three-dimensional net-shaped structure and comprising a foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde as base materials; and compressing means for compressing the ink absorbing member toward the ink feeding port. According to a sixth aspect of the present invention, there is provided a head cartridge including a printing head for ejecting ink therefrom and an ink tank for storably receiving therein ink to be fed to the printing head, the printing head and the ink tank being integrated with each other, wherein the ink tank comprises: a housing having an ink feeding port formed therethrough so as to allow ink to be storably received therein to be fed through the ink feeding port; an ink absorbing member accommodated in the housing for retaining ink therein, the ink absorbing member being a porous block having a three-dimensional net-shaped structure and comprising a foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde as base materials; and compressing means for compressing the ink absorbing member in the housing at least in one direction. According to a seventh aspect of the present invention, there is provided an ink jet printing apparatus for performing a printing operation by ejecting ink to a printing medium from a printing head adapted to eject ink therefrom, wherein the ink jet apparatus includes an ink tank for storably receiving ink to be fed to the printing head, the ink tank comprising; a housing having an ink feeding port formed therethrough so as to allow ink to be storably received therein to be fed through the ink feeding port; an ink absorbing member accommodated in the housing for retaining ink therein, the ink absorbing member being a porous block having a three-dimensional net-shaped structure and comprising a foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde as base materials; and compressing means for compressing the ink absorbing member toward the ink feeding port. According to an eighth aspect of the present invention, there is provided an ink jet printing apparatus for performing a printing operation by ejecting ink to a printing medium from a printing head adapted to eject ink therefrom, wherein the ink jet printing apparatus includes an ink tank for storably receiving therein ink to be fed to the printing head, the ink tank comprising; a housing having an ink feeding port formed therethrough so as to allow ink to be storably received therein to be fed through the ink feeding port; an ink absorbing member accommodated in the housing for retaining ink therein, the ink absorbing member being a porous block having a three-dimensional net-shaped structure and comprising a foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde as base materials; and compressing means for compressing the ink absorbing member in the housing at least in one direction. According to a ninth aspect of the present invention, there is provided an ink tank for storably receiving ink therein, comprising: an ink absorbing member having a porous three-dimensional divergent circuit network and comprising a thermosetting foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde as base materials; pressing means for pressing the ink absorbing member against an ink outflow portion; and alleviating means for alleviating an intensity of pressure applied to the ink absorbing member by the pressing means. According to an tenth aspect of the present invention, there is provided an ink tank, comprising: an ink absorbing member having a porous three-dimensional divergent circuit network and comprising a thermosetting foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde; and compensating means for applying a functional force to the thermosetting foamed block corresponding to deterioration of properties of the ink absorbing member. In the following the invention is further illustrated by embodiments with reference to the enclosed figures. Fig. 1A and Fig. 1B are schematic perspective views each of which shows the structure of a plurality of foamed cells for the purpose of explaining an principle of the present invention, respectively; Fig. 2 is a perspective view of an ink tank constructed according to a first embodiment of the present invention, showing the structure of the ink tank in the disassembled state; Fig. 3 is a perspective view of an ink tank constructed according to an embodiment modified from the first embodiment of the present invention, showing the structure of the ink tank in the disassembled state; Fig. 4 is a perspective view of an ink tank constructed according to a second embodiment of the present invention, showing the structure of the ink tank in the disassembled state; Fig. 5 is a perspective view of an ink tank constructed according to a comparative example which uses urethane foam, showing the structure of the ink tank in the disassembled state; Fig. 6 is a perspective view of an ink tank constructed according to an embodiment modified from the second embodiment of the present invention, showing the structure of the ink tank in the disassembled state; Fig. 7 is a perspective view of an ink tank constructed according to another embodiment modified from the second embodiment of the present invention, showing the structure of the ink tank in the disassembled state; Fig. 8 is a perspective view of an ink tank constructed according to further embodiment modified from the second embodiment of the present invention, showing the structure of the ink tank in the disassembled state; Fig. 9 is a perspective view of an ink tank constructed according to still further embodiment modified from the second embodiment of the present invention, showing the structure of the ink tank in the disassembled state; Fig. 10A and Fig. 10B are graphs each of which shows an advantageous effect obtainable from the structure of the ink tank shown in Fig. 8, respectively; Fig. 11 is a schematic sectional view of a head cartridge of the type integrated with an ink tank according to a third embodiment of the present invention, showing by way of example of the structure of the head cartridge; Fig. 12 is a schematic sectional view similar to Fig. 11, showing by way of comparative example of the structure of a head cartridge of the type integrated with an ink tank according to the third embodiment of the present invention; Fig. 13 is an illustrative sectional view of an ink tank shown in Fig. 11, showing how ink flows in the ink tank; Fig. 14 is an illustrative view which shows the distribution of a pore size measured with respect to a number of pores formed through an ink absorbing member accommodated in the ink tank while illustratively explaining how ink easily flows through the pores of the ink absorbing member in the ink tank; Fig. 15 is a schematic sectional view of a head cartridge of the type integrated with an ink tank according to an embodiment modified from the third embodiment of the present invention; Fig. 16 is a schematic sectional view of a head cartridge of the type integrated with an ink tank according to another embodiment modified from the third embodiment of the present invention; Fig. 17 is a schematic sectional view of a head cartridge of the type integrated with an ink tank according to further embodiment modified from the third embodiment of the present invention; Fig. 18 is a fragmentary schematic sectional view of a head cartridge of the type integrated with an ink tank according to still further embodiment modified from the third embodiment of the present invention; Fig. 19 is an illustrative view which shows the distribution of a pore size measured with respect to a number of pores formed through an ink absorbing member received in the ink tank while illustratively explaining how ink easily flows through the pores of the ink absorbing member in the ink tank; Fig. 20 is a fragmentary schematic sectional view of a head cartridge of the type integrated with an ink tank according to still further embodiment modified from the third embodiment of the present invention; Fig. 21 is a schematic sectional view of a head cartridge of the type integrated with an ink tank according to still further embodiment modified from the third embodiment of the present invention; Fig. 22 is a perspective view of an ink jet printing apparatus adapted to perform a printing operation using the head cartridge constructed according to each of several preferred embodiments of the present invention as mentioned above. (First Embodiment) In this embodiment, a foamed component molded of a melamine resin to be used as an ink absorbing member is prepared in the form of a porous member having a three-dimensional net-shaped structure, and it is provided as one of foamed substances each of which base material is a condensate composed of a compound having an amino group and a formaldehyde Generally, the three-dimensional net-shaped structure of the foregoing foamed component is built by using a number of comparatively fine single fibers, and it does not include any cell wall (film) Each single fiber has a relatively large length compared with its width or diameter Thus, a hollow portion (hereinafter referred to as a pore) of each cell has a large volume in the foamed component, causing the foamed component to exhibit a small volumetric density and a large volumetric efficiency. A pore size of the foamed component is comparatively uniformalized, and the pore rate represented by pores each having a pore size smaller than that of an average pore is comparatively small. In this embodiment, to assure that the foamed component is advantageously used, it is preferable that the volumetric efficiency of the foamed component is set to 95 % or more, the volumetric density of the same is set to 0.024 g/cm or less, and the average pore size is set to 200 µm or more. The foamed component as mentioned above can be produced by employing any one of hitherto known processes. In this embodiment, in the circumstances as mentioned above, the foamed component is compressed at least in the direction orienting toward an ink feeding port through which ink is fed to an ink jet head (hereinafter referred to as a printing head). The foregoing fact will be described in more detail in the following manner. Specifically, as an ink jet printing apparatus performs a printing operation at a higher speed, the printing head is activated by a comparatively high frequency (3 kHz or more) for ejecting ink therefrom, causing a quantity of ink to be ejected from an opening for a unit time to be increased. In this case, when the ink received in an ink tank is not fed to the printing head as the latter is activated by a high frequency, an optimum image can not be formed on a printing paper. In this embodiment, to cope with the foregoing problem, a intensity of capillary force is reduced by enlarging the pore size of the foamed component molded of a melamine resin, and moreover, reducing resistance against flowing of the ink in the foamed component. However, once the intensity of capillary force is reduced, there arise problems that a quantity of ink capable of being storably received in the ink tank without any occurrence of ink leakage is reduced, and moreover, the number of printing papers capable of being printed is also reduced. The foregoing problems can be eliminated by compressing the foamed component in the ink tank at least in the direction orienting toward the ink feeding port. Fig. 1A and Fig. 1B are schematic perspective views each of which shows a part constituting the foamed component molded of a melamine resin, respectively. Fig. 1A shows by way of perspective view the structure of the foamed component designated by reference numeral 12 before the latter is compressed. As is apparent from the drawing, each cell in the foamed component 12 is composed by combining horizontally extending single fibers 120h with vertically, extending single fibers 120v and includes pore opening portions 121h and pore opening portions 121v. Fig. 1B shows by way of perspective view the state that the melamine foamed component 12 is compressed in the A arrow-marked direction. As is apparent from the drawing, each of the pore opening portions 121v orienting at a right angle relative to the A arrow-marked direction shown in Fig. 1A has a reduced opening area due to the foregoing compression but an opening area of each of the pore opening portions 121h is not reduced irrespective of the compression. While the melamine foamed component 12 is kept in the compressed state as mentioned above, the capillary force exhibits certain directionality or the directionality of the capillary force is increased. Thus, when the ink held in each pore is displaced to the feeding port side under the influence of a negative pressure or an atmospheric pressure applied to the printing head, the ink retaining force induced by the capillary force to act as resistance against the displacement of the ink is enlarged in the direction at a right angle relative to the compressing direction attributable to variation of the opening area of each pore opening portion 121v but it hardly varies in the compressing direction. Consequently, the pore size as measured in the ink feeding direction is enlarged so as to allow the ink to be quickly fed while an intensity of ink retaining force is reduced, and a necessary ink retaining power effective in the other direction can be obtained. With respect to a conventional foamed component molded of a polyurethane resin, when it is compressed in the same manner as mentioned above, the ink retaining force of the foamed component does not exhibit remarkable variation of directionality or an intensity of ink retaining power is not, enlarged so far. This is attributable to the fact that thin films remaining still in structural members constituting the urethane foamed component are superimposed one above another when it is compressed, causing an area (projected area) of each opening portion orienting in the compressing direction to be reduced, whereby an intensity of ink retaining force effective in the compressing direction is enlarged. Fig. 2 is a schematic perspective view of an ink tank constructed according to the first embodiment of the present invention, particularly showing the structure of the ink tank in the disassembled state. A printing head 14 is connected to the fore end surface of a housing 11 of the ink tank. As is hitherto known, the printing head 14 may detachably be connected to the housing 11 of the ink tank. Alternatively, the printing head 14 may immovably be integrated with the housing 11 of the ink tank. In addition, a feeding port 13 is formed through the housing 11 of the ink tank at the central part of the connected surface between the housing 11 of the ink tank and the printing head 14 so as to enable ink to be fed from the ink tank to the printing head 14 therethrough. In this embodiment, the printing head 14 ejects ink therefrom by the functional force induced by the formation of a bubble as thermal energy is applied to the ink. A foamed component 12 molded of a melamine resin to serve as an ink absorbing member is fully accommodated in the housing 11 of the ink tank, and a length C of the accommodating portion of the housing 11 of the ink tank as measured in the ink feeding direction is dimensioned to be smaller than a length c of the melamine foamed component 12 as measured in the same direction. Thus, the melamine foamed component 12 can fully be accommodated in the housing 11 of the ink tank, and when the rear surface of the housing 11 of the ink tank is sealably closed with a cover 15, the melamine foamed component 12 is compressed by the cover 15 in the ink feeding direction. Although the foamed component 12 is compressed in the direction orienting toward the feeding port 13 in the above-described manner, an intensity of capillary force effective in the ink feeding direction is not enlarged because there is not any possibility that a pore size of the foamed component measured in the direction orienting toward the ink feeding port 13 is not reduced. This leads to the result that resistance against flowing of ink is not increased by any means. On the other hand, since a pore size of the foamed component 12 measured in the direction orienting at a right angle relative to the ink feeding direction is reduced, the intensity of capillary force effective in the last-mentioned direction is enlarged, resulting in a desired intensity of ink retaining force being obtainable. With this construction, a quantity of initially charged ink does not decrease, and moreover, there does arise a malfunction that ink leaks outside of the housing 11 through an environment communication pore 16 or the like. Fig. 3 is a perspective view similar to Fig. 2 wherein an ink tank is constructed according to an embodiment modified from the first embodiment of the present invention. In this embodiment, a plurality of grooves radially extending from the ink feeding port 13 are formed on the inner wall surface of the fore wall of the housing 11 in order to allow ink to promotively flow toward the ink feeding port 13. The relationship among a pore size of the foamed component available in this embodiment, a compression rate of the foamed component required for assuring a desired intensity of ink retaining force and resistance against flowing of the ink at this time is shown in Table 1. Pore size Compression rate for assuring a predetermined intensity of ink retaining force Resistance against flowing of ink Comparative Example 180-200 (µm) 1 100% Embodiments 200-240 (µm) 1.4 about 83% 240-280 (µm) 1.8 about 71% 280-320 (µm) 2.2 about 45% As is apparent from Table 1, in this embodiment, in the case that the melamine foamed block having a pore size, of 200 to 320 µm in the uncompressed state is used at a compression rate of 1.4 to 2.2, a predetermined intensity of ink retaining force, i.e., an intensity of ink retaining force assuring a desired quantity of charged ink without any occurrence of ink leakage can be obtained, and moreover, it is possible to set resistance against the flowing of ink in the compressing direction to about 83 % or less in the case that the foamed block is not compressed (i.e., in the case that a compression rate of the foamed block assumes a value of 1). It should be noted that the pore size departing from the foregoing range of pore size but assuring that a desired effect can be expected by carrying out the present invention is exemplified by 150 to 450 (µm) in the uncompressed state, more preferably, 200 to 400 (µm). In the case that the pore size is enlarged within the aforementioned range, a certain degree of pore size can be assured regardless of partial breakage or injury of each single fiber. Thus, the reduction of ink feeding ability can be minimized. On the contrary, in the case that the pore size is set to 100 µm or less, desired reduction of the resisting against the flowing of ink can not be obtained with the ink tank. Thus, the ink tank can not practically be used when the printing head is driven at a high ejection frequency. In the case that the pore size is set to 500 µm or more, the compression rate should be set to 3 or more in order to assure that a desired intensity of ink retaining force can be obtained. However, this can not practically be realized for the reason associated with the structural conditions of the ink tank. In addition, there is a possibility that each single fiber constituting the melamine foamed block is often broken or damaged, resulting in mechanical properties of the melamine foamed block being degraded. A melamine constituting the foamed block used in this embodiment is a compound having an amino group, and at least one kind of material selected from a group consisting of urea, carboxylic acid amide, dicyandiamode, guanidine, sulfonic acid amide, aliphatic amine, benzoguana and its derivative can be used as a compound similar to the melamine resin. Besides formaldehyde, at least one kind of material selected from a group consisting of acetaldehyde, trimethylaldehyde, acrolein, benzaldehyde, fluflore, glyoxal, phthalaldehyde and terephthalaldehyde may be contained in the melamine based compound. The resultant ink absorbing block is prepared in the form of a porous block having a three-dimensional net-shaped structure, and the foregoing porous block is an elastic foamed block which is molded of a condensate composed of a melamine and a formaldehyde as a base material. This elastic foamed block can be produced by employing a method as disclosed in the document US-A-4,540,717. In addition, it is preferable that the resultant foamed block is prepared in the form of an elastic foamed block containing 80 % or more of condensate composed of melamine and formaldehyde The condensate composed of melamine and formaldehyde may contain a compound having other type of amino group by a quantity of 50 to 20 % by weight in addition to the melamine Alternatively, it may contain other type of aldehyde of 50 to 20 % by weight in the condensed state in addition to the formaldehyde. According to the first embodiment of the present invention as described above, an occurrence of malfunction that the ink absorbing block is permanently or excessively warped can be compensated or suppressed. In other words, the aforementioned problems associated with the ink tank have been satisfactorily solved by improving the structure of the ink absorbing block itself under a condition that the ink tank includes a mechanism for deformably accommodating a foamed block therein. (Second Embodiment) In contrast with the melamine foamed block constructed according to the first embodiment of the present invention, this embodiment is intended to optimize the structure of an ink tank in consideration of material properties of the foamed block, an ink feeding direction, a quantity of ink storably received in the ink tank and other factors. Fig. 4 is a perspective view of an ink tank constructed according to a second embodiment of the present invention, particularly showing the structure of the ink tank in the disassembled state. Referring to Fig. 4, a melamine foamed block (hereinafter referred to a melamine foam) 212 is fully accommodated in a housing 211. A melamine foam insert opening portion of the ink housing 211 kept open to the outside is sealably closed with a housing cover 215, and an environment communicating port 216 is formed through the housing cover 215 so as to enable an environmental air to be substituted from the consumed ink. A printing head 214 attached to the housing 211 serves to eject ink droplets to perform a printing operation with the ejected ink droplets in the same manner as the first embodiment of the present invention. As ink is ejected from the printing head 214, ink is continuously fed to the printing head 214 through an ink feeding port 213 projected slightly inside of the inner wall surface of the housing 211. Referring to Fig. 4, when a height of the housing 211 is designated by A , a width of the same is designated by B, a length of the same is designated by C, a height of the melamine foam 212 is designated by a , a width of the same is designates by b and a length of the same is designated by c, the following relationship is established among these dimensions. Firstly, a ratio of c/C represents a compression rate of the ink absorbing block 212 as measured in the ink feeding direction in the same manner as the first embodiment of the present invention. In this connection, the relationship between the compression rate and a quality of printed image established in this embodiment is shown in Table 2. dimensional ratio of c/C <1.0 1.0 1.2 1.5 1.8 Quality of printed image in terms of density occurrence of stopping of ink feed good good good reduced density As shown in Table 2, in this embodiment, each printing operation can excellently be achieved when the ratio of c/C assumes a value of 1 or more but 1.5 or less in the state that the relationship between other dimensions, i.e., a and b is modified in such a manner these dimensions to be reduced. Secondarily, the dimensions a , b, A and B are determined to satisfactorily establish the relationship as represented by the following inequality. 0.8 ≤ a / A x b/B ≤ 1.7 Data on performances of the ink tank obtained from a comparison made under a condition that the dimensional ratio among the above dimensions is changed are shown in Table (wherein the dimensions c and C are unchangeably determined such that the ratio of c/C assumes a predetermined value). Specifically, the dimensions of the housing 211 are unchangeably determined such that A is set to 3 cm, B is set to 2 cm and C is set to 4.5 cm but the dimensions a and b of the melamine foamed block 212 are changed. 0.7 0.8 1.0 1.3 1.7 2.0 Quantity of ink available 17g 20g 25g 25g 23g 20g Quality of printed image in terms of density good good good good good reduced density Occurrence of dust particles when foamed block is accommodated none none none small small large Referring to Table 3, a quantity of ink available for each printing operation is represented by the following equation. (quantity of ink available for printing operation) = (quantity of ink capable of being charged in foamed block) - (quantity of ink remaining in foamed block) Referring to Table 3 again, in the case that a product of a / A x b/B is smaller than 0.8, as a volume of the foamed block 212 itself is considerably reduced, a quantity of ink capable of being initially retained is correspondingly reduced. This leads to the result that a quantity of ink available for each printing operation is reduced. When the value representing the foregoing product is larger than 1.75, an intensity of ink retaining force of the foamed block 212 is enlarged, resulting the ink feeding ability of the foamed block 212 being degraded. Consequently, the foamed block 212 becomes unsuitable for the printing head 214 when the latter is driven at a high ejection frequency, and moreover, it becomes practically difficult to feed ink to the printing head 214, causing a quantity of ink remaining in the foamed block 212 to be increased. Thus, a quantity of ink available for each printing operation is reduced. Next, with respect to the density of printed image and the quality of the same, in the case that the value representing the foregoing product is larger than 2.0, the ink feeding ability of the foamed block 212 is reduced and the density of printed image is likewise reduced. The dust particles arising when the foamed block 212 is accommodated in the housing 211 as shown in Table 3 represent cut pieces appearing from the melamine foamed block 212 due to frictional rubbing between the foamed block 212 and the housing 211 not only when the foamed block 212 is accommodated in the housing 211 but also after the former is accommodated in the latter. It should be noted that the appearance of the dust particles as mentioned above is caused attributable to comparatively hard and brittle properties of the melamine foamed block 212. To prevent the foamed block 212 from being partially broken or damaged not only when the foamed block 212 is accommodated in the housing 211 but also after the former is accommodated in the latter, it is recommendable that the inner wall surface of the housing 211 and the outer surface of the foamed block 212 are coated with a surface active agent and a slip additive. Specifically, in this embodiment, to prevent the foamed block 212 from being partially broken or damaged or to compensate or suppress the deterioration of properties of the foamed block 212, the housing 211 and/or the foamed block 212 are subjected to various kind of preliminary treatment. For example, slidability is preliminarily given to the slidable surface of the housing 211 and/or the foamed block 212 before the foamed block 212 is accommodated in the housing 211. To prevent the foamed block 212 itself from being partially broken or damaged, each cut surface of the foamed block 212 is processed in such a manner as to exhibit excellent smoothness. In addition, various kinds of compensative treatments for compensating the deterioration of properties of the ink absorbing member, i.e., the foamed block 212 (inclusive of treatment for giving a water repelling property to the hydrophilic foamed block 212, treatment for strengthening the structure of the same and treatment for improving the durability of the same) are conducted for the ink tank. It is preferable that typical preliminary treatment is conducted for the ink tank in such a manner that the housing 211 and/or the foamed block 212 is coated with a surface active agent, a slip additive, a water repelling agent or the like. The surface active agent is exemplified by a negative ion type surface active agent, a positive ion type surface active agent, an amphoteric type surface active agent and a non-ion type surface active agent. Alternatively, a fluorine based surface active agent may be employed for the same purpose. Generally, an oil based lubricant is used as a slip additive. For example, a dibasic acid ester, a silicone or the like is preferably employable as a slip additive. In addition, a manganese disulfate and a steatite are employable as a solid type slip additive, and a grease or the like is employable as a semisolid type slip additive. Additionally, a polyethylene grycerode is preferably used as a water soluble type slip additive because it has few effect on an ink to be used. It should be noted that water and the ink itself to be used can serves as a slip additive. A high molecular compound having a large number of molecules compared with that of the surface active agent is employable as a water repelling agent, and it is preferable to use a fluorine-containing high molecular compound as a water repelling agent. It should be noted that at least the surface located opposite to the ink feeding port on the housing 211 is processed by employing a water jet process in order to satisfactorily achieve a printing operation with remarkable reduction of the generation of dust particles. When it is assumed that substantial inner dimensions of the housing 211 are designated by A and B and outer dimensions of the foamed block 212 are designated by a and b, a dimensional ratio defining the inner tank is determined to establish the relationship represented by the following inequality. 0.8 ≤ a / A x b/B ≤ 1.7 Fig. 5 is a perspective view of an ink tank constructed according to a comparative example from the second embodiment of the present invention as shown in Fig. 4, particularly showing by way of comparative example the structure of the ink tank in the disassembled state. In this example, a formed block 222 molded of a polyurethane resin serves as an ink absorbent. Specifically, the ink tank includes a foamed block 222 and a housing 221 in which the foamed block 222 is accommodated, and when the latter is practically accommodated in the housing 221, a volume of the foamed block 222 is compressed in the housing 221 at a comparatively large compression rate (ranging from 3 to 5). The reason why the compression rate is determined to assume a large value as mentioned above consists in that reliability of the ink tank against an occurrence of leakage or a similar malfunction is assured. Generally, a desired intensity of ink retaining force is realized by compressing the foamed block 222 having a low intensity of ink retaining force in the non-compressed state so as to reduce a pore size of the foamed block 222, causing an intensity of capillary force of the foamed block 222 effective for retaining ink in the latter to be enlarged. In the case that a foamed block molded of a melamine resin is used for the ink tank like in the preceding embodiment, since the melamine foamed block exhibits a high hydrophilic property compared with the urethane foamed block, it is possible to assure a sufficiently high intensity of ink retaining force without any necessity for enlarging the compression rate as mentioned above. Fig. 6 is a perspective view of an ink tank constructed according to another embodiment modified from the second embodiment of the present invention shown in Fig. 4, particularly showing by way of example the state that the function of the ink tank is substantially improved. The ink tank includes a foamed block 262 molded of a melamine resin and a housing 261 in which the foamed block 262 is accommodated. In this embodiment, a plurality of ribs 267 each extending toward the ink feeding port 263 side are formed on the inner wall surface of the ink housing 261. With this construction, a plurality of atmospheric air flowing paths each extending in the forward direction to reach the left-hand wall of the housing 261 are maintained in the housing 261, whereby as the ink retained in the foamed block 262 is consumed, an atmospheric air flowing through an atmospheric air communication port 266 is stably substituted for the consumed ink. In this embodiment, a substantial dimension of the housing 261 as measured in the vertical direction is designated by A in the drawing (i.e., a distance between the lower ends of the upper ribs 267 and the upper ends of the lower ribs 267). In addition, to facilitate inflow of an environmental air in the housing 261 from the outside, ribs 268 are formed on a cover 268. As described above, according to the second embodiment of the present invention, while the ink absorbing block is accommodated in the housing in the operative state compressed at least in one direction, the compression rate of the ink absorbing block is adequately determined, and moreover, a quantity of ink initially charged in the ink absorbing block and an ink feeding ability of the ink tank are satisfactorily determined. Consequently, there hardly arises a malfunction that the ink absorbing block is partially broken or damaged due to frictional rubbing between the housing and the foamed block. (Modified Example 1 of Second Embodiment) Fig. 7 is a perspective view of an ink tank constructed according to an embodiment modified from the second embodiment of the present invention, particularly showing the structure of the ink tank in the disassembled state. Referring to Fig. 7, while a foamed block 232 molded of a melamine resin is accommodated in a housing 231, a dimension a2 of the foamed block 232 located remote from an ink feeding port 233 is determined to be smaller than a dimension a1 of the same located in the proximity of the same so that the foamed block 232 has a certain gradient across the length of the foamed block along the upper surface of the same between both the dimensions a1 and a2. With such construction, while the foamed block 232 is accommodated in the housing 233, a cell size of the foamed block 232 is distributed such that a number of cells are forcibly formed in such a manner as to allow the cell size to become smaller as the measuring position approaches toward the ink feeding port 233 more and more. As a result, since an intensity of ink retaining force becomes higher toward the ink feeding port 233, ink can stably be fed to a printing head 234 attached to the fore surface of the housing 231. Incidentally, in contrast with the foamed block 232, the same advantageous effects as mentioned above can be obtained also in the case that inner dimensions of the housing 231 are determined in such a manner as to allow them to become smaller toward the ink feeding port 236. (Modified Example 2 of Second Embodiment 2) Fig. 8 is a perspective view of an ink tank constructed according to another embodiment modified from the second embodiment of the present invention, particularly showing the structure of the ink tank in the disassembled state. Referring to Fig. 8, the ink tank includes a foamed block 242 molded of a melamine resin and a housing 241 in which the foamed block 242 is accommodated, and a number of holes 247 each extending from an atmosphere communicating port 243 side toward an ink feeding port 246 side are formed through the foamed block 242 in the longitudinal direction. With this construction, lattices (composed of fibers) forming a number of cells in the foamed block 242 are separated from each other, causing a part of the foamed block 242 having an enlarged pore size to be forcibly formed. Consequently, ink can stably be fed to a printing head 244 attached to the fore surface of the housing 241. The extension of each hole 247 from the atmosphere communicating port 246 side toward the ink feeding port 243 side is intended to assure that ink is easily displaced toward the ink feeding port 243 because a part of the ink is displaced through the holes 247 formed in the foamed block 242. Fig. 10A and Fig. 10B are graphs each of which shows an advantageous effect obtainable from the structure of the ink tank shown in Fig. 8, particularly showing the degree of improvement in respect of fluctuation of a printed image density every production lot before the holes 247 are formed through the foamed block 242 (Fig. 10A) and after they are formed through the same (Fig. 10B), respectively. As is apparent from these graphs, variability of the printed image density in a product is remarkably reduced after the holes 247 are formed through the foamed block 242 in the above-described manner. (Modified Embodiment 3 of Second Embodiment) Fig. 9 is a perspective view of an ink tank constructed according to another embodiment modified from the second embodiment of the present invention, particularly showing the structure of the ink tank in the disassembled state. Referring to Fig. 9, the ink tank includes a foamed block 252 molded of a melamine resin and a housing 251 in which the foamed block 252 is accommodated, and a plurality of slits 257 each extending from an atmosphere communicating port 253 side toward an ink feeding port 256 side are formed in the foamed block 252 in the longitudinal direction. With this construction, lattices each forming a cell in the foamed block 252 are separated from each other, causing a pore size in the slit portion to be forcibly largely dimensioned in the foamed block 252. Consequently, ink can stably be fed to a printing head 254 attached to the fore surface of the foamed block 252. In each of the aforementioned embodiments, to prevent the printing head from being separated from the ink absorbing member, resilient thrusting means such as a spring (a coil spring, a leaf spring or the like) may be disposed in the ink tank so as to allow a certain intensity of resilient force to act on them. This leads to the result that a function for bringing the printing head in close contact with the ink absorbing foamed block can be improved, and moreover, the foregoing function can continuously be maintained with the aid of the resilient thrusting means. The present invention has been described above with respect to the first embodiment, the second embodiment and the three modified embodiments wherein the ink feeding port is disposed at the central part of the fore surface of the housing of the ink tank but it should of course be understood that the present invention should not be limited only to these embodiments. For example, in case that the present invention is applied to an ink feeding port which is disposed at a predetermined position offset from the central part of the fore surface of the housing, it is recommendable that the foamed block is slantwise compressed toward the ink feeding port by suitably establishing the relationship between a contour of the foamed block and the housing and a size of each of them. Otherwise, the ink absorbing block is compressed along ink paths formed through the ink absorbing member. As is apparent from the above description, in each of the aforementioned embodiments, since the foamed block defining the ink absorbing member in the ink tank is compressed in the direction orienting toward the ink feeding port, a pore size of the foamed block as measured in the foregoing direction does not vary but a pore size of the same as measured in the direction orienting at a right angle relative to the foregoing direction is dimensionally reduced. In the circumstances as mentioned above, when each pore size of the foamed block is preliminarily dimensionally enlarged, an intensity of capillary force effective in the compressing direction, i.e., in the direction orienting toward the ink feeding port can be determined to be comparative low, while an intensity of capillary force effective in the direction orienting at a right angle relative to the aforementioned direction can be enlarged. Thus, an ink feeding property can be improved while a predetermined intensity of capillary force is maintained but an intensity of ink retaining force of the foamed block effective in the ink feeding direction is reduced. Since the ink absorbing member is accommodated in the housing in the compressed state, the ink absorbing member and the housing are brought in close contact with each other at all times. Especially, since the ink absorbing member is brought in close contact with the ink feeding port, there does not arise a malfunction that a gap such as an air layer or the like is formed in the ink feeding paths. As a result, ink can adequately be fed with the ink tank including the melamine foamed block as an ink absorbing member, especially by activating the printing head at a high ejection frequency. (Third Embodiment) This embodiment is concerned with the structure of an ink tank and the structure of an ink outflow portion for feeding ink from the ink tank to a printing head in the case that an ink absorbing member molded of a melamine-formaldehyde condensate is used for the ink tank in the same manner as each of the aforementioned embodiments. Fig. 11 is a schematic sectional view of an ink absorbing member, i.e., a head cartridge of the type integrated with an ink tank constructed according to a third embodiment of the present invention, showing by way of example the structure of the head cartridge. In this embodiment, a printing head designated by reference character H includes liquid paths 401 which are arranged in the direction orienting at a right angle relative to the plane of the drawing and which correspond to a plurality of ink ejecting openings 401A. To generate energy required for ejecting ink from the ink ejecting openings 401A, it is recommendable to employ an electrothermal converting element for heating ink so as to generate a bubble with the ink in order to achieve ink ejection under the influence of the pressure induced by the bubble, an electromechanical converting element, e.g., a piezoelectric element for generating vibrations in ink or the like. The ink is fed via an ink feeding tube 402 from an ink tank 405 secured to the head H with a base plate 403 interposed therebetween to the liquid paths 401 or a common liquid chamber 401C communicated with the liquid paths 401. The lower end of the ink feeding tube 402 serves as an ink outflow port of the ink tank 405, and a filter 404 is disposed at the ink outflow port of the ink tank 405. The filter 404 serves to prevent the liquid path 401 and associated components from being clogged with dust particles involved in an ink absorbing member, causing a quality of printed image to be degraded. In addition, the filter 404 serves to prevent small bubbles present in the ink absorbing member from reaching each liquid path 401 to induce a malfunction that ink is incorrectly ejected from the ink ejecting openings 401A. It is preferable that an opening area of the ink outflow port is determined to assume a large value not only in consideration of the number of liquid paths 401, dimensions of each liquid path 401 and a frequency employable for driving the foregoing energy generating element but also in consideration of the fact that as a quantity of ink passing through each liquid path 401 per unit time increases, a property of frequency responsiveness is degraded. On the other hand, in the case that a filter is disposed at the ink outflow portion of an ink tank like in the embodiment, to assure that an ink tank is produced at an inexpensive cost, it is required from the viewpoint of a production cost that the filter is designed to have small dimensions as far as possible. To satisfactorily meet the foregoing requirement, it is acceptable that an opening area of the ink outflow portion of the ink tank is adequately determined. In this embodiment, the filter 404 is disposed at the ink outflow portion of the ink tank in such a manner as to come in pressure contact with an ink absorbing member 407 having high elasticity. Thus, the filter 404 itself is brought in close contact with the ink absorbing member 407. Alternatively, the filter 404 may be disposed at the intermediate position of an ink feeding tube 402 which extends in the printing head H to reach the liquid paths 401. A metallic material, a synthetic resin or the like can be used as a structural material constituting the filter 404. In this embodiment, the ink absorbing member 408 basically composed of a number of single fibers is accommodated in the ink tank 405. The ink absorbing member 408 includes a porous three-dimensional divergent circuit network molded of a thermosetting melamine condensate or the like having no cell film formed therein as described in each of the aforementioned embodiments. That is, the ink absorbing member 408 is constructed of a thermosetting foamed block molded of a condensate composed of a compound having an amino group and a formaldehyde as a base material. Since the ink absorbing member 408 composed of a number of single fibers has no cell film formed therein, an advantageous effect of the ink absorbing member 408 is that a very small quantity of ink remains in the ink absorbing member 408 after completion of a recording operation performed using the ink storably received in the ink tank 405. In contrast, in the case that an ink absorbing member is molded of a foamed polyurethane resin which is hitherto usually used as a raw material, a cell film is formed in the ink absorbing member. Thus, ink is liable to adhere to the remaining film portion, causing ink having a quantity of about 10 to 20 % based on an initially charged quantity to finally uselessly remain in the ink absorbing member. For this reason, it is preferable to employ an ink absorbing member made of a number of single fibers like the ink absorbing member 408 for an ink absorbing block serving as an ink impregnant. In this embodiment, two ink absorbing blocks 407 each molded of a foamed polyurethane resin while exhibiting high elasticity or two members each having high elasticity are accommodated in the ink tank 405 in addition to the ink absorbing member 408 made of a number of single fibers. The positions where the ink absorbing blocks 407 are accommodated in the ink tank 405 in that way are determined to be positionally coincident with those where a high intensity of pressure is applied to the ink absorbing member 408. In this embodiment, the position where one of the ink absorbing blocks 407, i.e., the upper ink absorbing block 407 is accommodated in the ink tank 405 is positionally coincident with an ink outflow portion or a pressure contact portion where the ink absorbing block 407 comes in pressure contact with the ink absorbing member 408. In addition, in this embodiment, a plurality of ribs 406 are formed on the bottom wall of the ink tank 405 in such a manner as to allow the ink absorbing block 407 to apply a certain intensity of pressure to the ink absorbing member 408 from below while coming in pressure contact with the latter. Specifically, in this embodiment, the filter 404 disposed at the lower end of the ink feeding tube 402 positionally coincident with the ink outflow portion of the ink absorbing member 408 serves as first pressing means effective for pressing the ink absorbing member 408 from above, and moreover, the ribs 406 serve as second pressing means effective for pressing the ink absorbing member 408 from below. In practice, a various kind of material exhibiting poor elasticity is employed for the ink absorbing member 408 made of a number single fibers. For example, in the case that the ink absorbing member 408 is molded of a thermosetting melamine condensate, when a high intensity of pressure is applied to the ink absorbing member 408, i.e., when the filter 404 or the ink outflow portion is brought directly in pressure contact with the ink absorbing member 408 as shown in Fig. 14, there arises a malfunction that a three-dimensional divergent circuit network of the ink absorbing member 408 is broken or damaged and, after the pressure disappears, it can not be restored to the original configuration, resulting in permanent deformation occurring with the ink absorbing member 408. In this embodiment, the two ink absorbing blocks 407 each having excellent elasticity are arranged at the positions located opposite to the ink outflow portion and the ribs 406 so as to allow the ink absorbing blocks 407 to be elastically deformed due to close contact with projected parts of the ink outflow portion and the ribs 406 in order to attenuate the pressure applied to the ink absorbing member 408. With this construction, the ink absorbing member 408 is hardly deformed without any possibility that the structure thereof is broken or damaged. Next, a necessity for bringing the ink absorbing member in pressure contact with the ink outflow portion or the filter 404 disposed in the ink absorbing member will be described below with reference to Fig. 13 and Fig. 14. Fig. 13 is an illustrative sectional view of an ink tank 405 constructed according to the third embodiment of the present invention, particularly showing how ink flow in the ink tank, and Fig. 14 is a graph which shows the distribution of a pore size measured with respect to a number of pores formed through an ink absorbing member received in the ink tank while illustratively explaining how ink easily flows through the pores of the ink absorbing member in the ink tank. A pore size of each of the pores formed in the ink absorbing member is dimensioned to largely fluctuate due to various conditions associated with production of ink tanks. In this connection, a mechanism for retaining ink in the ink absorbing member is operated by the action of a capillary force given by each pore. As is apparent from a principle representing a capillary phenomenon, the smaller the pore size, the higher the intensity of force effective for absorbing ink in each pore. Since the pore size fluctuates in that way, an intensity of ink absorbing force correspondingly fluctuates in such a manner as to allow ink to remain in the region where each pore is dimensioned to have a small pore size (i.e., the region where the capillary power exhibits a high intensity) with a problem that it is difficult that the ink flows out of the pore in the course of consumption of the ink. While the foregoing state is unchangeably maintained, an ink consumption efficiency is degraded. The part defined by hatched lines in Fig. 14 represents the state that the filter is not brought in pressure contact with the ink absorbing member. At this time, the capillary power of the ink absorbing member uniformly fluctuates in the ink tank. This leads to the result that any force effective for displacing ink in the direction orienting toward the filter is not generated by the capillary force derived from each pore but the flowing of ink to be fed to the recording head H is achieved mainly by the negative force arising in the printing head side. In this embodiment, to cope with the foregoing malfunction, since the ink absorbing blocks 407 each having high elasticity and the ink absorbing member 408 made of single fibers are brought in pressure contact with the ink outflow portion or the filter 404, the pore size can forcibly be changed by the foregoing pressure contact regardless of how the pore size fluctuates, whereby the direction of displacement of the ink can be oriented toward the ink outflow portion side as illustrated by arrow marks in Fig. 13. Distribution of the pore size in the ink absorbing member constructed in the above-described manner is represented by solid lines each having a comparatively large width in Fig. 14. As is apparent from the drawing, a force effective for allowing the ink to be collected in the vicinity of the ink outflow portion having a small pore size, i.e., a high intensity of capillary force is generated by compressing the ink absorbing member in such a manner that the pore size becomes smaller than the smallest pore size employable when the ink absorbing member is used in the non-compressed state. In addition, when the ink absorbing blocks 407 each having a pore size smaller than that of the ink absorbing member 408 is used, a quantity of ink remaining after completion of the practical use of the ink tank can be reduced, resulting in an ink use efficiency being increased. In the case that the ink absorbing member is used in the uncompressed state, ink is caused to flow only by the gravity weight thereof. For this reason, the position assumed by the ink outflow portion relative to the ink tank is restrictively determined in such a manner as to allow the ink outflow portion to be substantially oriented in the downward direction. In contrast with the foregoing case, according to the fourth embodiment of the present invention, ink can be fed to the ink outflow portion not only in the upward direction but also in the transverse direction. In other words, limitative restriction on an attitude to be assumed when an ink tank or a head cartridge is used for performing a recording operation can be alleviated. As is apparent from the above description, it is very advantageously effective that the ink absorbing member made of single fibers is adequately compressed. However, in the case that an ink absorbing member made of single fibers while exhibiting low elasticity is brought directly in pressure contact with the filter or the ink outflow portion in the same manner as the ink absorbing member having high elasticity, structural breakage occurs with the ink absorbing member. Thus, there arise malfunctions that the contour of each pore is undesirably deformed, the capillary force is hardly generated, and the filter is covered with pulverized fiber particles, causing it to clogged with them. In this embodiment, a plurality of ribs 406 are formed on the bottom wall of the ink tank 406 so as to allow the ink absorbing member 408 made of single fibers to be pressed against the filter 407. Thus, a high intensity of pressure is generated by the ribs 406 while the ink absorbing block 407 having high elasticity is interposed between the ribs 406 and the ink absorbing member 408 made of single fibers. In the case that any structural breakage does not occur or the pressure having such a low intensity that no particular problem appears with the ink absorbing member 408 is applied to the latter like in the case that the pressing member has a wide pressing area, there does not arise a necessity for arranging an ink absorbing block having a high elasticity for the ink absorbing member 408. This case is exemplified by the case that a certain intensity of compressing force is applied to the inner wall surface of the ink tank located on the opposite side relative to the ink outflow portion or the filter 404 without any formation of the ribs 406 on the bottom wall of the ink tank. Alternatively, the compressing force may be applied to the inner wall surface of the ink tank other than the foregoing one in order to assure that ink adequately flows in the ink absorbing member 408. Otherwise, inner dimensions of the ink tank may be determined to be appreciably smaller than outer dimensions of the ink absorbing member 408 in order to assure that the ink absorbing member 408 is accommodated in the ink tank in the adequately compressed state. The aforementioned facts are equally applicable to embodiments modified from the third embodiment of the present invention. (Modified Embodiment of the Third Embodiment) Fig. 15 shows by way of schematic sectional view the structure of a head cartridge of the type integrated with an ink tank according to an embodiment modified from the third embodiment of the present invention wherein a plurality of compression coil springs are used as second pressing means for pressing an ink absorbing member against a filter or an ink outflow portion of the ink tank. In this embodiment, the pressing force given by the springs 411 is applied to an ink absorbing member 408 made of single fibers via a plate-shaped member 410 having a comparative wide area. According to this modified embodiment, the pressing force can be accurately adjusted. The second pressing means should not be limited only to the compression coil springs as shown in the drawing. Any type of suitable member can be employed in place of the compression coil springs, provided that it is proven that it can utilize an elastic restoring force given by a material constituting the foregoing member. For example, a leaf spring made of a metallic material, a synthetic resin or the like, an air pressure spring or the like can be noted as second thrusting means. (Modified Embodiment 2 of the Third Embodiment) Fig. 16 shows by way of schematic sectional view the structure of a head cartridge of the type integrated with an ink tank according to another embodiment modified from the third embodiment of the present invention wherein an ink outflow portion or a filter 409 having a substantially semispherical contour is disposed in the ink tank. This embodiment is intended to prevent an ink absorbing member from being broken or damaged due to stress concentration along an edge portion of the ink outflow portion or the filter 409 when the latter is pressed against the ink absorbing member. With this construction, the ink outflow portion or the filter 409 can be brought in direct contact with an ink absorbing member 408 made of single fibers but not with an ink absorbing block 407 having high elasticity. (Modified Embodiment 3 of the Third Embodiment) Fig. 17 shows by way of schematic sectional view the structure of a head cartridge of the type integrated with an ink tank according to another embodiment modified from the third embodiment of the present invention wherein a filter collision portion of the ink tank adapted to come in contact with an ink absorbing member 408 having an area larger than that of an ink outflow portion or a filter 404. An area required by the filter 404 is determined by a value preset for an ink flow rate, and it is preferable from the viewpoint of a production cost that the foregoing area is set to a necessary minimum limitative value. When a quantity of thrusting of the filter 404 against the ink absorbing member 408 is increased so as to obtain an effect for compressing the ink absorbing member 408 with the filter 404 having small dimensions, a large magnitude of load is exerted on the ink absorbing member 408. In this embodiment, to cope with the foregoing malfunction, a sufficiently large compressive volume of the ink absorbing member 408 can be maintained while suppressibly reducing an intensity of stress acting on the ink absorbing member 408 by determining a dimension b of the filter collision part larger than a dimension a of the filter 404. This makes it possible to press the ink outflow portion or the filter 404 directly against the ink absorbing member 408 made of single fibers but not against an ink absorbing block 407 having high elasticity. Usually, the filter collision part having a dimension b includes an allowance smaller than 1 mm in association with an effective area of the filter 404 having a dimension a for enabling ink to practically pass therethrough. An operational effect of the filter 404 can substantially be improved by determining the foregoing allowance of the filter collision part to assume a value of 1 mm or more. (Modified Embodiment 3 of the Third Embodiment) Fig. 18 shows by way of schematic sectional view the structure of a head cartridge of the type integrated with a ink tank according to further embodiment modified from the third embodiment of the present invention wherein a quantity L of thrusting of the filter collision part of a filter 404 against an ink absorbing member 408 made of single fibers is determined based on a diameter W of a fictitious circle defining the filter collision part of the filter 404 by way of convertible calculation. As described above with reference to Fig. 14, the larger the quantity L of thrusting of the filter collision part of the filter 404 is, the higher the operational efficiency of ink consumption is. However, in the case that the filter 404 has a small width compared with the thrusting quantity L, there is a danger that the fibrous structure of the ink absorbing member is broken or damaged. In view of this fact, it is desirable that the relationship between the thrusting quantity L and the diameter W of the fictitious circle, i.e., a ratio of W/L is set to 10 or less. To assure that an ink consumption efficiency is increased by the compressing effect of the ink absorbing member, it is acceptable that the thrusting quantity L is enlarged. In practice, the extent of enlargement of the thrusting quantity L is determined depending on fluctuation of a pore size in the ink absorbing member 408. In the case that the ink absorbing member 408 is molded of, e.g., a melamine resin so as to allow it to have a pore size ranging from about 50 µm to 250 µm, it is desirable that the ratio of W/L is set to 0.1 or more. Thus, when the ratio of W/L lies within the range represented by an inequality of 0.1 ≤ W/L ≤ 10 , fluctuation of an intensity of capillary force arising in the vicinity of the filter can be enlarged much more fluctuation of the capillary force attributable to fluctuation of the pore size as shown in Fig. 19. Consequently, an ink consumption efficiency of the ink absorbing member 408 can be improved. (Modified Embodiment 4 of the Third Embodiment) Fig. 20 shows by way of fragmentary schematic sectional view the structure of a head cartridge of the type integrated with an ink tank according to further another embodiment modified from the third embodiment of the present invention wherein an ink absorbing member is compressed in a different manner. In this embodiment, a member 411 for supporting a filter 404 is displaceably held in an ink tank so that the filter 404 is brought in pressure contact with an ink absorbing member 408 by the resilient force given by a plurality of filter pressing springs 410. With this construction, the same advantageous effects as those in each of the aforementioned embodiments can be obtained with the head cartridge. In addition, the same effect for compressing the ink absorbing member as mentioned above can be obtained by employing a plurality of resilient members for the filter. (Modified Embodiment 5 of the Third Embodiment) Fig. 21 shows by way of schematic sectional view the structure of a head cartridge of the type integrated with an ink tank according to still further embodiment modified from the third embodiment of the present invention wherein an ink consumption efficiency is substantially improved. In the case that a filter 404 is disposed in the vicinity of the inner wall surface of an ink tank 405, a stress is liable to appear in an ink absorbing member 408 molded of, e.g., a melamine resin having low elasticity while exhibiting a steep gradient. In this embodiment, a filter portion is disposed at the position located at the substantially same distance as measured from the respective inner wall surfaces of an ink tank 405, whereby any stress does not appear in the ink absorbing member 408 with a steep gradient. Thus, the ink absorbing member 408 is satisfactorily protested from damage or injury, and the ink absorbing member 408 can be compressed at a high efficiency. In each of the third embodiment and the embodiments modified from the latter, one end of the ink feeding tube is inserted into the ink tank, and the ink outflow portion or the filter disposed in the latter is brought in close contact with the ink absorbing member so as to allow it to serve as thrusting means. However, the present invention should not be limited only to this. Alternatively, e.g., a hole formed through one side wall of the ink tank may be substituted for the ink outflow portion. In this case, it is acceptable that thrusting means such as a spring, a rib or the like is disposed in the hole. For example, the spring or the rib serving as second thrusting means employed for the embodiment as shown in Fig. 11 and Fig. 15 can be used as thrusting means to be disposed in the foregoing hole. When the technical concept of the present invention is examined from other viewpoint, properties of the ink absorbing member made of single fibers are liable to be deteriorated due to so-called warpage or the like, and as they are deteriorated, an ink feeding ability of the ink absorbing member is correspondingly deteriorated. To compensate the deterioration of the ink absorbing ability of the ink absorbing member, it is advantageously effective to dispose compensating means for applying a functional force to an ink absorbing foamed block while compensating the foregoing deterioration, i.e., compensating means for applying to the ink absorbing foamed block the functional force effective for collectively feeding ink to the ink outflow portion to maintain the ink feeding ability. In practice, the compensating means of the foregoing type is employed for carrying out the present invention. In each of the aforementioned embodiments, the ink absorbing block disposed in the vicinity of the ink outflow portion while exhibiting elastic properties more excellent than those of the ink absorbing member made of single fibers or a capillary force having an intensity higher than that of the ink absorbing member as shown in Fig. 11 or Fig. 15 or the spring for thrusting the ink absorbing member while following the variation of a contour of the ink absorbing member as shown in Fig. 15 corresponds to the aforementioned compensating means. However, it is obvious that the compensating means may be designed in other different manner rather than the foregoing one. As is apparent from the above description, according to each of the third embodiment of the present invention and the embodiments modified from the latter, the following advantageous effects can be obtained by adequately pressing the ink outflow portion against the ink absorbing member with the aid of the pressing means as mentioned above. 1. Since the ink absorbing member made of single fibers while exhibiting a high ink consumption efficiency and excellent easiness of allowing it to be filled with ink can be employed as an ink absorbing member to be accommodated in the ink tank, a printing head can be produced at a reduced cost, and moreover, it can practically be used at a low running cost. 2. Since a capillary force can be generated with the ink absorbing member while exhibiting a certain gradient in terms of an intensity thereof, the ink absorbing member made of single fibers can practically be used at an increased ink consumption efficiency. 3. Since the degree of freedom is increased in respect of the direction of ink outflow from the ink tank, a printing head or a printing unit can be designed and constructed with an improved degree of freedom. Fig. 22 is a perspective view of an ink jet printing apparatus adapted to perform a printing operation using a head cartridge constructed according to each of the embodiments and the modified embodiments of the present invention as mentioned above. In the drawing reference numeral 109 designates a head cartridge including an ink tank and a printing head integrated with each other, and reference numeral 111 designates a carriage having the head cartridge 109 mounted thereon to perform a scanning operation in the S arrow-marked direction. Reference numeral 113 designates a hook for securing the head cartridge 109 to the carriage 111, and reference numeral 115 designates a lever for actuating the hook 113. A plurality of markers 117 are impressed on the lever 115 for enabling the position where a printing operation is performed with the printing head at present and the position where the lever 115 has been actuated to be visually read by a user based on a plurality of calibrations recessed on a cover (not shown) for the ink jet printing apparatus. Reference numeral 119 designates a support plate for supporting electrical connecting portions to be electrically connected to the head cartridge 109, and reference numeral 121 designates a flexible cable for electrically connecting the electrical connecting portions to a main controlling ink absorbing member for the ink jet recording apparatus. Reference numeral 123 designates a guide shaft for guiding the reciprocable displacement of the carriage 111 in the S arrow-marked direction. The guide shaft 123 is inserted through a bearing 125 of the carriage 111. Reference numeral 127 designates an endless timing belt fixedly secured to the carriage 111 for transmitting a power required for reciprocably displacing the carriage 111 in the S arrow-marked direction. The timing belt 127 is spanned between a pair of pulleys 129A and 129B disposed on the opposite sides of the ink jet printing apparatus. A certain intensity of driving power is transmitted from a carriage motor 131 to the right-hand pulley 129B via a power transmitting mechanism including gears and others. Reference numeral 133 designates a conveyance roller for conveying a printing medium such as a paper or the like while restrictively defining a printing plane of the printing medium. The conveyance roller 133 is rotationally driven by a conveyance motor 135. Reference numeral 137 designates a paper pan for bringing the printing medium to the printing position from the paper feeding tray 104 side, and reference numeral 139 designates a feed roller disposed at the intermediate position located on a feeding path for the printing medium for conveying the printing paper while thrusting the latter against the conveyance rollers 133. Reference numeral 134 designates a platen located opposite to an ink ejecting port of the head cartridge 109 for restrictively defining the printing plane of the printing medium, and reference numeral 141 designates a paper discharging roller disposed at the position located downstream of the printing position as seen in the printing medium conveying direction for discharging the printing medium toward a paper discharging port (not shown). Reference numeral 142 designates a pulley disposed opposite to the paper discharging roller 141 for generating a conveying power required for conveying the printing medium in cooperation with the paper discharging roller 141 while thrusting the latter via the printing medium, and reference numeral 143 designates a releasing lever for releasing the feed roller 139, a retaining plate 145 and the pulley 142 from the thrusted state. Reference numeral 145 designates a retaining plate disposed for suppressively preventing the printing medium from being floated up at the position located in the printing position. In the shown case, a printing head adapted to perform a printing operation by ejecting ink is employed for the ink jet printing apparatus. Thus, a distance between the ink ejecting port forming plane of the printing head and the printing plane of the printing medium is comparatively small, and moreover, since the foregoing distance should strictly be controlled in order to preventing the printing medium from coming in contact with the ink ejecting port forming plane, it is advantageously acceptable that the retaining plate 145 is disposed in the above-described manner. Reference numeral 147 designates a series of calibrations impressed on the retaining plate 145, and reference numeral 149 designates a marker formed on the carriage 111 to correspond to one of the calibrations 147. With this construction, the position where each printing operation is performed with the printing head and the position where the printing head is mounted for the ink jet printing apparatus can visually be read by a user with the aid of the calibrations 147 and the marker 149. Reference numeral 151 designates a cap disposed opposite to the ink ejecting port forming plane of the printing head. The cap 151 is molded of an elastic material such as a rubber or the like, and it is supported in such a manner as to enable it to be brought in contact with the ink ejecting port on the printing head and then released from the contact state relative to the printing head. The cap 151 is used for the purpose of protecting the printing head from damage or injury or allowing the printing head to be subjected to suction recovering treatment when no printing operation is performed with the printing head. The suction recovering treatment represents a treatment to be executed in such a manner that the cap 151 is located opposite to the ink ejecting port forming plane of the printing head and ink is then ejected from the ink ejecting port by activating the energy generating element disposed inside of the ink ejecting port for generating energy to be utilized for the purpose of ink ejection whereby a factor of causing incorrect ink ejection due to the presence of bubbles, dust particles or ink having an increased viscosity unsuitably employable for each printing operation is eliminated. In addition, the suction recovering treatment represents another treatment to be executed in such a manner that a factor of causing incorrect ink ejection is eliminated by forcibly ejecting ink from the ink ejecting port while the ink ejecting plane of the printing head is covered with the cap 151. Reference numeral 153 designates a pump for allowing a suction force effective for forcibly ejecting ink from the ink ejecting port to be applied to the printing head, and moreover, sucking the extra ink received in the cap 151 for executing suction recovering treatment subsequent to the forcible ink ejection or suction recovering treatment subsequent to preliminary ink ejection. Reference numeral 155 designates a waste ink tank in which waste ink sucked by the pump 153 is storably received, and reference numeral 157 designates a tube for making communication between the pump 153 and the waste ink tank 155. Reference numeral 159 designates a blade for wiping the ink ejecting port forming plate of the printing head. The blade 159 is supported in such a manner as to be displaced to the position where a wiping operation is performed in the course of displacement of the printing head while the blade 159 is projected toward the printing head side as well as the position where the blade 159 is retracted away from the ink ejecting port forming plane of the printing head without any contact with the latter. Reference numeral 161 designates a motor, and reference numeral 163 designates a cam assembly for driving the pump 153 and displacing the cap 151 and the blade 159 with the driving power transmitted from the motor 161. The first and second embodiments of the present invention have been described above with respect to the case where the ink feeding portion is disposed at the central part on a predetermined side wall of the ink tank housing. However, it is obvious that the present invention should not be applied only to the foregoing type of ink tank. Specifically, in the case that the ink feeding portion is disposed at the position deviated from the foregoing central part of the predetermined side wall of the ink tank housing, the foamed block may slantwise be compressed toward the ink feeding portion on the assumption that the relationship between a contour of each of the foamed block and the housing and dimensions each defining the same is adequately determined. Alternatively, the foamed block may be compressed toward the ink feeding portion in conformity with the extension of an ink path in the ink absorbing member. A length c of the melamine foamed block 12 to be accommodated in the ink tank housing 11 as measured in the longitudinal direction is dimensioned to be larger than a length C of the ink tank housing 11 as measured in the longitudinal direction. Thus, while the foamed block 12 is accommodated in the ink tank housing 11, it is compressed in the direction orienting toward the ink feeding port 13 from which ink is fed to the printing head 14, i.e., in the ink feeding direction. Consequently, the ink retaining force induced by the capillary force is not intensified in the compressing direction of the melamine foamed block 12, resulting in an ink feeding capability of the printing head 14 being improved. On the contrary, the ink retaining force effective at a right angle relative to the compressing direction of the melamine foamed block 12 is intensified.

Claims: An ink tank (405; 501) for storably receiving ink therein, comprising a housing (11; 211; 261; 231; 241; 251) having an ink feeding port (13; 213; 263; 233; 243; 253; 502) formed therethrough so as to allow ink to be storably received in said housing to be fed through said ink feeding port; an ink absorbing member (12; 212; 262; 232; 242; 252; 301; 308; 408; F) accommodated in said housing for retaining ink therein, said ink absorbing member being a porous member having a three-dimensional net-shaped structure and is molded of a condensate composed of a compound having an amino group and a formaldehyde as base materials; and a compression means (15; 215; 265; 235; 245; 255; 406; 410; 411) for compressing said ink absorbing member, characterized in that the ink absorbing member is compressed such that the ink retaining force effective in the compressing direction is not intensified. An ink tank according to claim 1, characterized in that said compressing means compresses said ink absorbing member toward said ink feeding port. An ink tank according to claim 1 or 2, characterized in that said compressing means compresses said ink absorbing member in said housing at least in one direction. An ink tank according to any of claims 1 to 3, characterized in that said compressing means is constructed such that dimensions defining at least a part of the contour of said ink absorbing member are larger than those defining a part of the inner contour of said housing so as to enable said compressing to be achieved. An ink tank according to any of claims 1 to 4, characterized in that said compound having an amino group is at least one kind of material selected from a group consisting of melamine, urea, carboxylic acid amide, dicyandiamido, guanidine, sulfonic acid amide, aliphatic amine, benzoguana and its derivatives. An ink tank according to any of claims 1 to 5, characterized in that said ink tank is used for an ink jet printing head adapted to perform a printing operation at an ink injecting frequency of 3 kHz or more. An ink tank according to any of claims 1 to 6, characterized in that when it is assumed that inner dimensions on a plane including said ink feeding port (213) in said housing (211) as measured in the substantially vertical and transverse directions are designated by A and B and outer dimensions on a plane of said ink absorbing member (212) extending in parallel with the first-mentioned plane including said ink feeding port (213) as measured in the vertical and transverse directions before said ink absorbing member (212) is accommodated in said housing (211) are designated by a and b, the dimensional relationship represented by the following inequality is established among said dimensions A, B, a and b. 0.8 ≤ a / A x b/B ≤ 1.7. An ink tank according to any of claims 1 to 7, characterized in that while the contour of said ink absorbing member (212) is maintained, a / A and/or b/B are maximized on said plane located on an ink feeding port side. An ink tank according to any of claims 1 to 8, characterized in that a plurality of cutouts, slits or holes (247) each extending toward said ink feeding port (243) are formed in said ink absorbing member (212). An ink tank according to any of claims 1 to 9, characterized in that a part of said housing (241) along which said ink absorbing member (212) and the inner wall of said housing come in contact with each other is coated with a surface active agent and a slip additive. An ink tank according to any of claims 1 to 10, characterized by a foamed member deforming/accommodating means for compensating or suppressing deterioration of properties of said ink absorbing member. An ink tank according to any of claims 1 to 11, characterized in that at least a part of said ink absorbing member accommodated in said housing for retaining ink therein being subjected to preliminary treatment for the purpose of compensation the deterioration of property of the ink absorbing member. An ink tank according to any of claims 1 to 12, characterized in that at least a side surface of said ink absorbing member on the ink feeding side or a slidable surface of said ink absorbing member after the latter is accommodated in said housing is subjected to water jet working. An ink tank according to any of claims 1 to 13, characterized by a pressing means (404) for pressing said ink absorbing member (408) against an ink outflow portion; and an alleviating means (407; 409) for alleviating an intensity of pressure applied to said ink absorbing member by said pressing means. An ink tank according to claim 14, characterized in that said pressing means (404) includes an ink feeding tube (402) adapted to be brought in close contact with said ink absorbing member (408) together with said ink outflow portion. An ink tank according to claim 14 or 15, characterized in that a filter (404) is disposed in said ink outflow portion. An ink tank according to any of claims 14 to 16, characterized in that said alleviating means includes a second ink absorbing member (407) having high elasticity at least at the pressed part of the interior of said ink tank, said second ink absorbing member (407) being interposed between said ink absorbing member (408) and said ink outflow portion. An ink tank according to claim 14 to 17, characterized in that said alleviating means is an ink outflow portion (409) convexly projected toward said ink absorbing member. An ink tank according to claim 14 to 18, characterized in that said alleviating means is a collision portion adapted to collide against said ink absorbing member (408), said collision portion having dimensions larger than those of said ink outflow portion. An ink tank according to any of claims 14 to 19, characterized in that said alleviating means is a collision portion having a ratio of W/L ranging from 0.1 to 1.0 on the assumption that a squeezing length of said ink outflow portion squeezed in said ink absorbing member by said pressing means is designated by L and a diameter of the circle derived from convertible calculation made for an area of the collided part of said collision portion on the said ink absorbing member is designated by W. An ink tank according to any of claims 14 to 20, characterized by a second pressing means (406; 411) for additionally pressing said ink absorbing member (408) toward said ink outflow portion so as to reliably maintain the thrusted state induced by said pressing means (404). An ink tank according to any of claims 14 to 21, characterized by a second alleviating means (407) for alleviating an intensity of pressure applied to said ink absorbing member (402) by said second pressing means (406). An ink tank according to any of claims 1 to 22, characterized by a compensating means (407; 410, 411) for applying a functional force to said thermosetting foamed member corresponding to deterioration of properties of said ink absorbing member. An ink tank according to claim 23, characterized in that said compensating means (407) comprises a foamed member having elastic properties and a capillary force more excellent than those of said thermosetting foamed block, said foamed member being interposed between the ink outflow portion side and said ink absorbing member (408). An ink tank according to claim 23 or 24, characterized in that said compensating means (410, 411) includes an elastic pressing mechanism for pressing said ink absorbing member (408) while following deterioration of properties of said ink absorbing member. A head cartridge (109) including a printing head (H) for ejecting ink therefrom and an ink tank according to any of claims 1 to 25, said printing head (H) and said ink tank being integrated with each other. A head cartridge (109) according to claim 26, characterized in that said printing head (H) generates a bubble by utilizing thermal energy, and subsequently, ejects ink therefrom by the functional force induced by said bubble. An ink jet printing apparatus for performing a printing operation by ejecting ink to a printing medium from a printing head (H) adapted to eject ink therefrom, characterized in that said ink jet apparatus includes an ink tank according to any of claims 1 to 25.

Inventors: HIGUMA MASAHIKO, ISHINAGA HIROYUKI, KAWAI JUN, MASUDA KAZUAKI, OHTA TOKUYA, OSADA TORACHIKA, SAITO TAKASHI, SATO YOHEI, SUGITANI HIROSHI, TANEYA YOICHI, HIGUMA, MASAHIKO, ISHINAGA, HIROYUKI, KAWAI, JUN, MASUDA, KAZUAKI, OHTA, TOKUYA, OSADA, TORACHIKA, SAITO, TAKASHI, SATO, YOHEI, SUGITANI, HIROSHI, TANEYA, YOICHI, HIGUMA, MASAHIKO, C/O CANON KABUSHIKI KAISHA, ISHINAGA, HIROYUKI, C/O CANON KABUSHIKI KAISHA, KAWAI, JUN, C/O CANON KABUSHIKI KAISHA, MASUDA, KAZUAKI, C/O CANON KABUSHIKI KAISHA, OHTA, TOKUYA, C/O CANON KABUSHIKI KAISHA, OSADA, TORACHIKA, C/O CANON KABUSHIKI KAISHA, SAITO, TAKASHI, C/O CANON KABUSHIKI KAISHA, SATO, YOHEI, C/O CANON KABUSHIKI KAISHA, SUGITANI, HIROSHI, C/O CANON KABUSHIKI KAISHA, TANEYA, YOICHI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1994
Main classification: B41J2
IPC codes: B41J2